Method of preparing keratin-containing films and coatings

ABSTRACT

Isolated keratin is dispersed in an alkaline medium consisting of alcohol and water. The dispersion is applied to solid substrates including food and dried to form an edible coating. The coating can be stripped from the substrate as a continuous film. A portion of a second proteinaceous substance and a plasticizer can be included in the dispersion.

United States Patent Anker [54] METHOD OF PREPARING KERATIN- CONTAININGFILMS AND COATINGS [72] Inventor: Charles A. Anker, Minneapolis, Minn.[73] Assignee: General Mills, Inc.

[22] Filed: Sept. 18, 1969 [21] Appl. No.: 859,198

[52] US. Cl ..99/166, 99/18, 99/169, 99/171 LP, 106/155, 106/161,117/164, 260/123], 264/212 [51] Int. Cl ..A23b 1/10, C08r 7/04 [58]Field ofSearch ..99/166,18,168,169,171LP; 106/155, 161,135, 311;117/164; 264/212; 260/123.7; 252/364, 311

[56] References Cited UNITED STATES PATENTS 2,445,028 7/1948 Jones eta1. ..106/155 2,427,857 9/1947 Hamill ..99/ 166 2,474,339 6/1949 Ward eta1. .....106/155 X 2,814,851 12/1957 Hervey ..106/155 X Feb. 115, 19722,158,481 5/1939 I-Iansenetal ..99/166UX 3,464,825 9/1969 Anker ..99/18OTHER PUBLICATIONS Chemicals Used in Food Processing, Nat. Academy ofSciences, 1965, page 265 Primary Examiner-Morris O. Wolk AssistantExaminer-Stephen B. Davis Att0rneyAnthony A. .luettner and Gene 0.Enockson [57] ABSTRACT Isolated keratin is dispersed in an alkalinemedium consisting of alcohol and water. The dispersion is applied tosolid substrates including food and dried to form an edible coating. Thecoating can be stripped from the substrate as a continuous film. Aportion of a second proteinaceous substance and a plasticizer can beincluded in the dispersion.

14 Claims, N0 Drawings The present invention relates to a new and usefulprocess for preparing films and coatings comprised of keratin. Thisinvention also relates to the resulting films and coated articles. Thefilms and coatings of this invention are strong and flexible and findnumerous uses, particularly in the food area.

Although solutions of keratin from various natural sources have beenproduced, these solutions have sometimes not been suited for producingfilms because of one or more problems. For example, some prior attemptsto produce a highly concentrated solution of keratin have givensolutions containing large amounts of undispersed keratin. Thesesolutions, because of their lack of homogeneity, tend to form weak filmswhen they are cast. Further, the removal of the undispersed fraction ofthe keratin source material to attempt to solve this problem has notbeen commercially feasible. In addition, some means heretofore known forpreparing keratin articles have not shown how to prepare keratinmaterials suitable for food applications.

l have discovered a new process of preparing films and coatings fromcertain concentrated, relatively homogeneous dispersions of keratin.Many of the films and coatings thus formed are found to be useful in avariety of food applications. The dispersions of keratin used in myprocess are made in various alcohol-water mixtures, and keratin coatingsand films are prepared therefrom by a commercially practicable means.

The films and coatings of this invention are essentially all protein.Thus, when reagents used in their preparation are selected so as to notinclude harmful or disagreeable chemicals, they are bland and edible.Further, no reagents are required in this invention which impartundesirable odors to the products.

This invention has commercial attractiveness for several reasons. Thekeratin used is very dispersible in the alkaline alcohol-water mixtures,and it is thus unnecessary to attempt to separate large amounts of theundispersed keratin from the dispersion. Temperatures above the boilingpoint of the alcohol-water mixtures are not necessary to disperse thekeratin, and thus high cost pressurized processing equipment is notrequired. A further advantage of this invention is that the dispersionsare not made directly from raw keratin sources, but are prepared frompurified keratin sources. The products therefrom may thus present acleaner appearance, nondispersible materials being essentially absent.

It is thus an object of the present invention to provide a new processwhereby keratin coatings and films are prepared from fluid, alkaline,relatively homogeneous dispersions of keratin in an alcohol-waterdispersing medium. It is also an object of this invention to providekeratin films and coatings prepared according to this new process. Afurther object is to provide various articles, and particularly foodarticles, which are wrapped, coated or encased by various of the keratinfilms and coatings. These and other objectives will become apparent inthe description which follows.

As indicated, the films and coatings of this invention are prepared fromdispersions comprising keratin. Keratin is one of the fibrous proteinsfound in various animals. Its essential function is to provideprotection to the bodies of organisms, and is commonly found to be aprincipal constituent of hair, hooves, feathers, hides and the like.Although keratin may be isolated from these and other natural sources,it is preferred for this invention to isolate keratin from poultryfeathers. The feathers may be whole or in ground form, althoughprocessing of the latter is generally more convenient.

The keratin useful in the process of the present invention can beisolated from the natural sources thereof by'various known procedureswhich preferably include the use of a reducing agent. The reducing agentappears to perform a variety of functions including increasing of thesolubility or dispersibility of the keratin and/or improving the odorand/or flavor of the recovered isolate. When used duringthe initialisolation step, the reducing agent apparently increases the solubilityor dispersibility of the keratin by breaking various disulfide bonds,both in the polypeptide chains (intrachain) and in the cross-linking ofdifferent polypeptide chains (interchain). When an alkali metal sulfideis used as the alkaline solubilizing agent, the keratin which issubsequently acid precipitated often has a bad odor indicating thathydrogen sulfide is being given off. Additionally, hydrogen sulfide maybe given ofiduring the precipitation step itself. In this instance, areducing agent, such as an alkali metal sulfite appears to not onlybreak some disulfide bonds but also to yield sulfurous acid which reactswith the hydrogen sulfide and any free sulfur formed during the sulfidesolubilization or subsequent precipitation of the keratin. The productsresulting from this reaction are theorized to be water soluble compoundssuch as H S O l-I S O and/or T1 8 0 These compounds are not volatile anddo not precipitate with the protein on addition of the acidprecipitating agent.

One preferred procedure for isolating the keratin, as indicated above,comprises extracting same from the natural sources with an aqueousalkali metal sulfide solution, treating the resulting aqueous extractwith an alkali metal sulfite and then precipitating the protein by theaddition of an acid. The resulting product may also be dried if desired.This process can be used to recover keratin protein from any naturallyoccurring keratin source material, and is particularly valuable in therecovery of high quality keratin protein from feathers.

The first step of this preferred procedure is to extract the keratinsource material with an aqueous solution of an alkali metal sulfide.Representative sulfides are sodium sulfide and potassium sulfide.Preferably the keratin source is in a relatively subdivided form topromote the extraction. For example, whole feathers can be extractedwith the sulfide solution but better extraction is obtained if thefeathers are cut into smaller pieces. The extraction is preferablycarried out at temperatures of about 20 to 50 C. The alkali metalsulfide is preferably used in an amount of about 2.5 to 20 percent byweight based on the weight of the material being extracted. It is alsopreferred to use relatively dilute solutions of the alkali metalsulfide. In this way the extracted keratin protein is more readilydissolved in the extracting medium. Thus the aqueous solutionspreferably contain from about 0.25 to 2 percent by weight of the alkalimetal sulfide and enough of the solution is used so that theconcentration of the extracted keratin protein therein remains belowabout 15 percent by weight, and is preferably in the range of l to 10percent by weight. Sodium sulfide (Na s) is the preferred extractant.

The protein containing solution is separated from the insoluble residueby conventional means such as decantation, filtration or the like. Theinsoluble residue can be further extracted or washed with water or freshaqueous sulfide solution and the resulting liquids can be treatedseparately or combined with the first obtained protein containingsolution. ln this way, the ultimate yield of protein is increasedsomewhat although the major amount of the protein is normally obtainedin the initial extraction step.

The protein containing solution is next treated with the alkali metalsulfite. Representative sulfites are sodium and potassium sulfite andbisulfite. A preferred treating agent is sodium sulfite (Na SO Thealkali metal bisulfites, such as sodium bisulfite (Na H are lesspreferred since they release sulfur dioxide at a faster rate and thusmay cause some localized premature precipitation unless added at aslower rate than the sodium sulfite. The sulfite is used in a molarexcess in relation to the amount of alkali metal sulfide used in theinitial extraction step. Preferably the molar ratio of the sulfite tothe sulfide is in the range of l.0l-l0.0:1.0. The sulfite in dry form orin the form of an aqueous solution thereof is simply added to theprotein-containing solution in the designated amount. Theprotein-containing solution can be stirred during or after the additionto effect a more uniform distribution of the sulfite therein.

After the described sulfite treating step, the protein is precipitatedby the addition of acid in the conventional manner. Any of a variety ofinorganic or organic acids can be used. Representative acids arehydrochloric acid, sulfuric acid, acetic acid, phosphoric acid and thelike. The acid is used in an amount sufficient to lower the pH of theprotein containing solution to the isoelectric point or below of theprotein. Preferably, the pH is reduced to below about 4.5 and the rangeof 3.0 to 4.5 is especially suitable.

The precipitated protein is separated from the protein barren liquid byconventional techniquesi.e., decantation, filtration and the like. Inall of the steps of the process the temperature is not critical but ispreferably in the range of 20 to 50 C.

The precipitated and separated protein can be dried if desired. Anyconventional drying technique can be usedi.e., spray, drum, tray, freezeor the like. The resulting keratin protein is a high quality producthaving good odor, color and flavor characteristics.

The following specific examples will serve to illustrate this preferredprocess of recovering the keratin from natural sources.

EXAMPLE A One hundred grams of cut turkey feathers were added to 1,333ml. of an aqueous solution of sodium sulfide (the solution consisted ofwater and 32 g. Na S-9H O). The resulting mixture was held at 40 C. for2 hours and then centrifuged for 20 minutes at 2,000 r.p.m. Thesupernatant liquid was decanted and saved. The residue was mixed with1,333 ml. water and then centrifuged as above. The second supernatantliquid was decanted and saved. The residue was discarded. Each of thesupernatant liquids was made 0.3 molar with respect to sodium sulfite(50.4 g. sodium sulfite added to each). The pH of each of the liquidswas adjusted to pH 4.2 by the addition of 6 N hydrochloric acid (thefirst required 81 ml. and the second 53 ml. of the acid). During theacidification of the liquids no hydrogen sulfide was liberated and nosulfur dioxide odor was noted. The resulting precipitates were separatedfrom the liquids by centrifugation and washed once with 0.01 Nhydrochloric acid (1 liter) and three times with 1 liter portions ofacetone. The protein was then allowed to air dry at room temperature.There was obtained 60.4 g. protein from the first supernatant liquid and8.1 g. protein from the second supernatant liquid. The protein was lightcolored, bland and substantially odor-free.

EXAMPLE B Keratin was isolated from chicken feathers by the followingpilot plant scale operation. Forty-five and one-half pounds of clean,dry chicken feathers were mixed with 75 gal. water containing 81 lb. ofcommercial grade sodium sulfide (60% Na S). The temperature of themixture was 103 F. The mixture was agitated for 2 hours and thetemperature of the resulting digest mixture was 98 F. The digest waspassed through a coarse screen to remove pieces of the undigestedfeather residue. To the digest was added 90 gal. water containing 23.6lb. commercial grade sodium sulfite. The pH of the digest was lowered to8.2 by adding 100 lb. 1 N hydrochloric acid. The digest was thenfiltered through a filter press using 28 lb. filter aid and a 1X] filtercloth. The filtering time was 2 hours. The clear amber filtratecollected was pH 8.7. To the filtrate was added 190 lb. 1 N HCl overabout 130 minutes to lower the pH to 4.2. The resulting proteinprecipitate was allowed to settle overnight, and the supernatant liquidwas removed. The precipitate was washed with 60 gal. water and allowedto settle in the supernatant wash water for hours, after which time thesupernatant liquid was removed. An additional 60 gal. water was added tothe precipitate and allowed to stand overnight. The supernatant liquidwas removed and the protein precipitate was collected by filtering. Theprotein cake thus formed was freeze dried to yield 11.55 lb. of drykeratin protein.

Additional processes or procedures other than the preferred onedescribed above, may be used to isolate keratin in a form suitable foruse in our invention. One such procedure involves digesting keratinsource materials (e.g., poultry feathers) in an alcohol-water mixturewhich contains ammonium sulfite. In another satisfactory process forobtaining keratin suitable for use in our invention, keratin sourcematerials are digested in a mercaptoethanol-alcohol-water mixture andfiltered to remove impurities, and the keratin is obtained bycentrifugation of the resulting gel mixture. In a further satisfactoryprocess of obtaining keratin, the latter method is followed, except thatthe mercaptoethanol-alcohol-water mixture is made alkaline by theaddition of a base such as sodium hydroxide, potassium hydroxide and thelike. In these procedures for isolating keratin, the ammonium sulfiteand mercaptoethanol reducing agents act primarily as aids for increasingthe solubility or dispersibility ofthe keratin protein.

The following examples will serve to illustrate these additionalsuitable processes we have used for obtaining keratin isolates useful inour invention.

EXAMPLE C A mixture consisting of 370 g. wet chicken feathers (200 g.,dry basis), 29.7 g. (NH SO -H O, 221 ml. 1 N hydrochloric acid, 715 ml.water and 1,1 10 ml. methyl alcohol was adjusted to a pH of 6 byaddition of 1 N NaOH and was heated to boiling and then refluxed for 40minutes. The mixture was then centrifuged to separate a liquid fraction.The resulting nonliquid portion of the mixture was a gellike mass. Tothis was added 1,000 ml. water and 1,000 ml. methyl alcohol, and theresulting mixture was heated to a boil and then filtered while hotthrough cheesecloth to remove undigested feather residue. This filteredmixture and the liquid fraction from the centrifugation step were eachheated to encourage homogeneity, and each mixture was adjusted to a pHof4.5 by addition of 1 N hydrochloric acid. The two mixtures wereallowed to stand overnight, and were then filtered together throughcheesecloth to remove the alcohol-water liquor and the keratin productthus isolated was dried in a vacuum oven. The yield was 129 g.

EXAMPLE D A mixture consisting of 370 g. wet chicken feathers (200 g.,dry basis), 1,830 ml. water, 2,000 ml. 95 percent ethyl alcohol and 20ml. mercaptoethanol was heated to C. and refluxed at that temperaturefor 20 minutes. The mixture was filtered while hot through cheeseclothto remove undigested feather residue. The filtered mixture was allowedto stand for about 60 hours, during which time the mixture assumed thecharacter of a white gel. This gel mixture was centrifuged to remove afraction of excess liquid, and was then vacuum dried at 50 C. The driedproduct was ground to a fine powder consistency. The yield was 105 g. ofisolated keratin.

EXAMPLE E A mixture of 370 g. wet chicken feathers (200 g., dry basis),2,230 ml. water, 9.6 g. sodium hydroxide, 1,600 ml. percent ethylalcohol and 40 ml. mercaptoethanol was heated to boiling and was heldthere for 20 minutes. The mixture was filtered while hot and centrifugedto remove undigested feather residue. The pH of the mixture was reducedto 6 to 7 by addition of 1 N hydrochloric acid, and the mixture wasallowed to stand overnight. The mixture, which had assumed a gellikecharacter, was centrifuged to remove excess solvents, and the solidsfraction was vacuum dried at 50 C., to yield 121.8 g. keratin.

EXAMPLE F Seven batches of keratin were removed from feathers accordingto the following procedure. A mixture of 200 g. dry feathers, 970 ml.water, 29.7 g. (NH SO;,'H O, 60 ml. 1 N

hydrochloric acid and 1,1 ml. 95 percent ethanol, having a pH of about6, was refluxed for 40 minutes. To the refluxed mixture were added 1,110ml. water and 1,1 10 ml. 95 percent ethanol. The resulting mixture wasfiltered while hot through cheesecloth and adjusted to a pH of 4.5 byaddition of hydrochloric acid. The mixture was allowed to cool and toset to a gel overnight, and was then centrifuged to remove excessliquid. The solids fraction after centrifugation was washed withportions of water and recentrifuged three times. The resulting keratinproduct was freeze dried. The total keratin thus isolated from the sevenbatches of feathers was ground to a fine powder consistency and weighed710 g.

The keratin films and coatings which are the products of the process ofthis invention are prepared from alkaline dispersions of keratin invarious alcohol-water mixtures.

The alcohols which are used to obtain the concentrated keratindispersions consist of various water soluble monohydroxy aliphaticalcohols containing one to four carbon atoms. lt is preferred to usesuch aliphatic alcohols which contain no more than three carbon atoms.

The water-alcohol ratio (volume basis) in the alkaline keratin solutionsis between about 0.211 to about 2.7:1. The weight ratio of protein toliquid, not including plasticizers, is between about 1:3 and 1:20 in thedispersion mixtures. At protein-liquid ratios greater than about 1:3, itis difficult to obtain homogeneous films and coatings. Where thekeratinliquid ratio is less than about 1:20, homogeneous products may beproduced but they tend to be thin and weak.

The alkalinity is provided in the keratin dispersions of this inventionby one or more of various water soluble inorganic bases, includingammonium hydroxide and a variety of metal hydroxides. Among thepreferred reagents of this type are ammonium hydroxide, sodium hydroxideand potassium hydroxide. The keratin dispersions have an alkaline pHwhich will be above 7.0 and up to 12 or higher.

A variety of ingredients may be included in the dispersions to impartincreased flexibility to the products prepared therefrom. Suchingredients may be termed plasticizers, and may include various polyolsand higher molecular weight alcohols such as glycerol, diglycerol,1,2,6-hexanetriol, triethanolamine, cetyl alcohol, mannitol, sorbitoland the like. Other soluble plasticizing agents employed in variousprotein uses may successfully be mixed in our dispersions. Thesematerials include various fatty acid derivatives, methacrylates andcitrates. Where food applications are sought for the products of thisinvention, plasticizers should not be used which would impartundesirable odor or taste to the products. Preferred plasticizerscomprise glycerol, diglycerol and 1,2,6- hexanetriol. For example,glycerol has been used in amounts up to about 60 percent of the weightof the protein, although amounts up to about 40 percent are preferred.

When no plasticizer is included in the keratin dispersion, initiallyflexible films and coatings may be produced. However, such products tendto become brittle upon drying. Thus, where it is desired to formproducts which retain their flexibility, it is necessary either toinclude a plasticizer in the dispersion or to subject the product to aplasticizing treatment. Where a plasticizer is included in in thedispersion, enough should be used that the desired flexibility isattained in the products. If too much plasticizer is used, the resultingkeratin containing films and coatings may tend to be weak, and theirsurfaces have an oily or greasy feel. Thus where a plasticizer isincluded, it is preferred that the weight ratio of protein toplasticizer be about 5:1 to 5:3.

When desired flexibility in the products is achieved by subjecting theproducts to a plasticizing treatment, means which bring the plasticizerin contact with such products will serve this result. For example, asolution of glycerol in water or ethanol provides a suitableplasticizing bath to which the keratin articles may be subjected. Thefilms and coatings of this invention may be plasticized subsequent totheir formation, for example, by immersing the same in a to 80 percentsolution of glycerol in water and/or ethanol.

To enhance the homogeneity of certain of the dispersion mixtures, theyare heated above room temperature. However, for various dispersionmixtures, good dispersion is obtained without heating. A dispersionmixture may be heated as high as its boiling point, which is about theboiling point of the alcohol-water azeotropic mixture employed. However,satisfactory dispersion is attained in some mixtures at temperaturesabove room temperature, but well under their respective boiling points.Thus where good dispersion does not occur at room temperature in one ofthe keratin dispersion mixtures used in my process, it is preferred toheat that mixture until the dispersion is complete, but to a temperaturenot exceeding the boiling point of the mixture at atmospheric pressure.

Where little or no reducing agent was used during the isolation of thekeratin, small amounts can be added to aid in the dispersing of thekeratin in the alcohol-water dispersing medium. Representative reducingagents are sodium sulfite, sodiurn bisulfite, ammonium sulfite andmercaptoethanol. When used, such reducing agent can be added in anamount of 0.1 to 5.0 percent by weight based on the weight of theprotein.

Although it is preferred to produce the films and coatings from keratinprotein alone, the same can be replaced by amounts of up to about 50percent by weight by a second protein or proteins provided that the filmor coating properties are not adversely affected to an excessive extent.The second protein may be selected from casein, zein, gelatin, oilseedproteins, fish proteins, leaf proteins and mixtures thereof.

The dispersions may be applied to various substrate surfaces or entirearticles by any of a number of methods wherein a relatively unifonncoating is obtained. Thus, for example, the dispersion may be sprayed orbrushed on the surface or the dispersion may be cast thereon using, forexample, a spreader bar. The surface or article may also be dipped intothe dispersion and then removed therefrom. Where the dried coating is tobe removed from the substrate surface as a film, it is preferred to usea substantially unreactive surface such as glass, stainless steel andvarious plastics. The surface should not be so smooth or nonreactivethat the surface tension of the dispersion tends to be greater than itsadhesion to the surface. Such surfaces will not be uniformly wetted bythe dispersion and will tend to give films of uneven thickness. Filmscan be stripped from more reactive surfaces by various physical meanssuch as sharp blades. And, of course, where the coating is to remain onthe surface such as when various foods including apple slices, candies,shelled nuts and the like are coated, it will often be desirable thatthe same firmly adheres to the surface or surfaces.

The coatings are allowed to dry to become solid and essentiallycontinuous. Drying or setting of the coatings may be hastened by meanscommonly used to encourage evaporation of the dispersing solvents-i.e.,by the use of a circulating stream of air or other gas and/or heat suchas obtained by various heaters including heat lamps. However, evenwithout such means to encourage more rapid drying, many of the coatingswill set up in a matter of minutes to a few hours at ambient roomtemperatures and pressures. The essentially continuous films andcoatings of the present invention can be of various thicknesses but willpreferably be from about 0.5 to 50 mils in thickness.

The following examples will serve to further illustrate the process andproducts of this invention.

EXAMPLE 1 To a mixture of 20 ml. water, 70 ml. ethyl alcohol and 2 ml. 6N ammonium hydroxide were added 4.8 g. glycerol and 12 g. dry keratinprepared from feathers as in Example B. The materials were heated to theboiling point (about 75 C.), and the resulting dispersion was clarifiedby centrifugation for 0.5 minute at 10,000 rpm. The dispersion wasallowed to cool to about 50 C., and films were cast on glass in air atambient room temperature. A spreader bar with a 6 mil gap was used toform the film. The film was pennitted to dry. The keratin film thusproduced was about 1 mil thick and was clear, strong, flexible andwithout objectionable odors.

EXAMPLE II To a mixture of 20 ml. water, 60 ml. 95 percent ethanol and 2ml. 6 N ammonium hydroxide was added 6 g. keratin prepared as in ExampleC. The mixture was heated for about 5 to minutes in a water bath untilthe keratin dissolved. Walnut halves without the shells, apple slicesand bark candy were dipped into the keratin dispersion and air dried ona screen. The coated objects all had a high gloss and no adverse flavordue to the coatings.

EXAMPLE III A mixture of 30 ml. water, 30 ml. 95 percent ethyl alcohol,1 ml. glycerol and 1 ml. concentrated ammonium hydroxide was used todisperse 5 g. feather keratin as prepared in Example C. The resultingdispersion was heated mildly and poured on a glass surface and allowedto dry at room temperature. A transparent flexible film was formed whichwas peeled from the glass surface.

EXAMPLE IV To a mixture of2 g. glycerol, 1 ml. 6 N ammonium hydroxide,ml. water and 15 ml. 95 percent ethyl alcohol was added 5 g. featherkeratin prepared as in Example B. The keratin dispersed upon mixing andheating to about 75 C. The heated dispersion was poured on a glasssurface where it rapidly thickened upon cooling to form a clear flexiblefilm which was removed from the glass.

EXAMPLE V A keratin dispersion was obtained from heating the followingmixture: 35 ml. water, 15 ml. 95 percent ethyl alcohol, 5 g. featherkeratin as prepared in Example C, 2 g. glycerol and 1 ml. 6 N ammoniumhydroxide. A clear flexible film was cast at room temperature on glass.

EXAMPLE VI To a solution of 30 ml. 95 percent ethyl alcohol and 30 ml.water were added and mixed 5 g. keratin as prepared in Example C and 3g. glycerol. Then 1 ml. ammonium hydroxide was added and the mixture washeated in a water bath to over 70 C. The resulting dispersion was pouredon a flat glass plate and cast into a film using a 0.006 inch gapspreader bar. The cast dispersion dried at room temperature to yield afilm which was easily removed from the glass. The film was very flexibleand was quite slippery to handle.

EXAMPLE VII To 5 g. feather keratin as prepared in Example C was added asolution of 10 ml. water, 30 ml. 95% ethanol, 2 ml. glycerol and 5 drops10 M sodium hydroxide. The resulting mixture was heated to help dispersethe keratin. A film cast from this mixture on a flat surface had aslight amber appearance and was ofgood strength.

EXAMPLE VIII A mixture was prepared consisting of 5 g. keratin preparedas in Example G, 2 g. glycerol, 10 ml. water, 2 ml. 6 N ammoniumhydroxide and 40 ml. 95 percent ethanol. The mixture was heated toboiling to disperse the keratin, and was cast or poured on a flat glassplate. Upon evaporation of excess dispersing medium from the castmixture, a strong and clear keratin film could be removed from the glassplate.

EXAMPLE IX Skinless wieners were spray coated with our keratindispersions according to the following procedure. A mixture was preparedconsisting of l2 g. feather keratin as prepared in Example C, 4 g.glycerol, 27 ml. water, 99 ml. percent ethanol and 6 ml. 0.5 N sodiumhydroxide. The mixture was heated to boiling to disperse the keratin. Aportion of the heated dispersed mixture was sprayed on skinless wienersusing a compressed air spraying device. The wieners were placed under aheat lamp to encourage evaporation of the dispersing medium. The wienerswere refrigerated for 3 hours and were then boiled. The keratin coatingadhered well to the wieners and the coated wieners had good eatingqualities.

EXAMPLE X A portion of the heated keratin dispersion mixture prepared inExample IX was sprayed, using a Paschke air brush, on one side each offour hamburger patties. The coatings on two of the patties were allowedto dry at ambient room conditions; these two coatings had a white opaqueappearance on drying. The remaining two patties were placed under a heatlamp to encourage drying of the keratin coatings; when dry, the coatingswere clear. The four patties were stored in a refrigerator for 3 hours.When they were stacked such that coated sides of adjacent patties werein contact, there was no sticking together of the patties when they wereunstacked. Two patties were broiled and two were fried. When the cookingof each patty was completed, whether the coated side was up or downduring cooking the coatings were not noticeable. The patty which wasfried with the coated side down did not stick to the frying pan. All ofthe patties had good eating characteristics.

EXAMPLE XI A 5 g. sample of the keratin as prepared in Example E wasadded to a solution containing 20 ml. water, 2 g. glycerol, 20 ml. 95percent ethyl alcohol and 1 ml. 6 N ammonium hydroxide. The mixture washeated to boiling to disperse the keratin. The dispersion was filteredwhile hot through a fine mesh stainless steel screen to remove anyundispersed keratin particles. The hot dispersion was cast to form filmson a flat glass plate using a 6 mil spreader bar. The film set up veryfast. When dry the films were peeled from the glass plate. The averagedry tensile strength of the film was 5,533 pounds per square inch. Theaverage wet tensile strength of the film after a 15 minute soak in waterwas 1,783 pounds per square inch.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. The process of coating a solid substrate which comprises: (1)applying to at least a portion of one surface thereof a coating ofafluid, relatively homogeneous, alkaline dispersion of a proteinaceoussubstance comprising at least about 50 percent by weight of isolatedkeratin protein in a dispersing medium consisting of alcohol and waterwherein the alcohol is a monohydroxy aliphatic alcohol of one to fourcarbon atoms, the dispersion obtains its alkalinity from a water solubleinorganic base, the weight ratio of protein to dispersing medium is inthe range of about 1:3 to 1:20, and the volume ratio of water to alcoholis in the range ofabout 0.2: l to 2.7: l; and (2) drying the coating onthe substrate.

2. The process of claim 1 wherein the water soluble inorganic base isselected from the group consisting of sodium hydroxide, potassiumhydroxide and ammonium hydroxide.

3. The process of claim 2 wherein the water soluble inorganic base isammonium hydroxide.

4. The process of claim 1 wherein the proteinaceous substance consistsof keratin protein.

5. The process of claim 4 wherein the keratin protein is isolated fromkeratin source materials by processes including the use ofa reducingagent.

6. The process of claim 1 wherein the monohydroxy aliphatic alcoholcontains one to three carbon atoms.

7. The process of claim 6 wherein the alcohol is ethanol.

8. The process of claim 1 wherein the dispersion also contains aplasticizer.

14. The process of claim 1 wherein the water soluble inorganic base isammonium hydroxide, the alcohol is ethanol, the proteinaceous substanceconsists of keratin protein, the keratin protein is isolated fromkeratin source materials by processes including the use of a reducingagent, the dispersion contains glycerol, the weight ratio of glycerol toprotein is in the range of about 5:1 to 5:3, the substrate has anessentially nonreactive surface and dried coating is (3) stripped fromthe substrate surface as a relatively continuous film.

2. The process of claim 1 wherein the water soluble inorganic base isselected from the group consisting of sodium hydroxide, potassiumhydroxide and ammonium hydroxide.
 3. The process of claim 2 wherein thewater soluble inorganic base is ammonium hydroxide.
 4. The process ofclaim 1 wherein the proteinaceous substance consists of keratin protein.5. The process of claim 4 wherein the keratin protein is isolated fromkeratin source materials by processes including the use of a reducingagent.
 6. The process of claim 1 wherein the monohydroxy aliphaticalcohol contains one to three carbon atoms.
 7. The process of claim 6wherein the alcohol is ethanol.
 8. The process of claim 1 wherein thedispersion also contains a plasticizer.
 9. The process of claim 8wherein the plasticizer is glycerol and the weight ratio of protein toglycerol is about 5:1 to 5:3.
 10. The process of claim 1 wherein theentire substrate is coated with the dispersion.
 11. The process of claim10 wherein the substrate is an edible food.
 12. The process of claim 1wherein the dried coating is (3) stripped from the substrate surface asa relatively continuous film.
 13. The process of claim 1 wherein thedried coating has a thickness of about 0.5 to 50 mils.
 14. The processof claim 1 wherein the water soluble inorganic base is ammoniumhydroxide, the alcohol is ethanol, the proteinaceous substance consistsof keratin protein, the keratin protein is isolated from keratin sourcematerials by processes including the use of a reducing agent, thedispersion contains glycerol, the weight ratio of glycerol to protein isin the range of about 5:1 to 5:3, the substrate has an essentiallynonreactive surface and dried coating is (3) stripped from the substratesurface as a relatively continuous film.